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The High Intensity heavy ion Accelerator Facility (HIAF) and Low Energy heavy ion Accelerator Facility (LEAF) of IMP are under construction. They will comprise many superconducting devices and components, such as magnets and current leads, with the superconducting materials covering NbTi, Nb3Sn and HTS. On the other hand, most of the superconducting devices have a high energy density and complex structure, requiring a targeted and active protection. In previous quench protection systems implemented at IMP, the quench detection was implemented in software or as microcontroller-based equipment, where power supplies in superconducting circuit provided quench detection functionality as well. These systems have some disadvantages, such as limited functionalities, poor reliability and high susceptibility to interference. Therefore, a new type of quench detection system (QDS) based on programmable FPGA and Isolated analogue input front-ends was developed to overcome these challenges. It is important to note that in the test facilities, there is no ionizing radiation, the QDS does not require radiation tolerance, thus a commercial programmable FPGA product was chosen as the development platform. The QDS is currently being put into operation, and some good results have been obtained in the cold tests of MCBRDP2 (belongs to HL-LHC, NbTi magnet) and FECR (belongs to LEAF, Nb3Sn magnet). Based on these successful applications, the new QDS has proven its functionality. The recorded data and practical experience also provided relevant information for the detection algorithms and functional upgrades. [ABSTRACT FROM AUTHOR]

In the design process of MRI magnets, the study of quench phenomenon is of great significance to the operation of superconducting magnets. In this paper, the quench characteristics of 1 T symmetric magnet and asymmetric magnet are simulated and analysed by using three-dimensional finite element software OPERA. The modelling process and algorithm of simulation are introduced in detail. The critical current density of NbTi superconducting material is set by looking up table variables preset by software. Through simulation and analysis, the changing principles of the current and resistance of the superconductor coil, which are important physical quantities of the two kinds of magnet structures in quenching are obtained. Three-dimensional simulation graphics are more conducive to observing the propagation speed of quench in different directions. It is concluded that although the DSV (diameter sphere volume) of asymmetric magnet is larger than that of symmetric magnet, the damage of asymmetric magnet is more serious than that of symmetric magnet during the quench. [ABSTRACT FROM AUTHOR]

A hypothesis shall be confirmed: Non-convergence of a series of numerical solutions, to simulate transient temperature under increasing losses in a superconductor, might tightly be correlated with the superconducting to normal conducting phase transition. Consider as an analogue a standard, mathematical power series expansion: While the exact limit cannot be captured within the series, there is no doubt about its existence. A series of numerical solutions in stability analysis is considered a parallel to the mathematical series convergence problem: Likewise, there is no doubt that a limit of the numerical solution series exists (the phase transition) but it cannot be reached within the series. The concept is applied to multi-filamentary BSCCO 2223 and coated, thin film YBaCuO 123 superconductors and to NbTi superconductor filaments. Support is provided by a microscopic stability model and from comparison of order parameters. Simulation of current transport near phase transitions may become severely in error if length of load steps is in conflict with time needed for its completion. [ABSTRACT FROM AUTHOR]

This paper addresses the applicability of the "additive approximation" of total thermal conductivity in heat transfer and in superconductor stability calculations. If cases (a), (b) and (c) denote total (conductive plus radiative), or only conductive or only radiative heat flux, respectively, each flux q ̇ calculated with Fourier's conduction law using the corresponding thermal conductivity (λa, λb, λc), the additive approximation would be confirmed if the heat flux difference Δ q ̇ = q ̇ a - q ̇ b - q ̇ c , at any position of an investigated object, and at any time, converges to zero. This is not trivial because of the strong, non-linear temperature dependence of the radiation component. Heat transfer calculations including radiative transfer are presented in this paper, first for simple, homogeneous, thin film test samples and later for a multi-filamentary BSCCO 2223 superconductor. The simulated heat sources either result from a sudden increase of conductor boundary temperature or from flux flow and Ohmic resistances in the superconductor under a disturbance (like transport current exceeding critcal current density). The conductors, though very thin, are non-transparent to mid-IR radiation. Validity of the additive approximation is critical for superconductor stability against quench. Based on the applied numerical scheme, a hypothesis is suggested concerning correlation of the results of the simulation (the "numerical space") with the experimental situation (the "physical reality"): Non-convergence of the numerical scheme might tightly be correlated with occurrence of a quench in the simulated superconductor. [ABSTRACT FROM AUTHOR]

Surface discharge can lead to the failures of insulation materials in LN2, especially when the bubbles are generated during the quenching process. In this paper, the surface discharge properties of polypropylene (PP)/boron nitride (BN) nanocomposites were investigated in the normal and quench conditions. The results showed that the surface discharge voltage was improved in the normal condition as the BN filler content was increased from 5 wt% to 10 wt%. But it was reduced as the BN filler content was 15 wt%. As the filler content was less than 10 wt%, the free charges were captured by traps, which were with deeper trap energy level. In quench condition, the bubbles were decreased as the BN filler content increased, which were associated with the higher thermal conductivity of BN to rapidly release the joule heat. Therefore, the surface discharge voltage was increased with the BN filler content. The research has the potential to restrain the surface discharges and extent the lifetime of insulation materials in high-temperature superconducting devices. [ABSTRACT FROM AUTHOR]

Protecting the magnets in case of a quench is a challenge for the 16 T superconducting dipole magnets presently designed for the 100 TeV: Future Circular Collider (FCC). These magnets are driven to the foreseen technological limits in terms of critical current, mechanical strength and quench protection. The magnets are protected with CLIQ (Coupling-Loss Induced Quench) system, which is a recently developed quench protection method based on discharging a capacitor bank across part of the winding. The oscillation of the magnet currents and the dissipation of the high stored energy into the windings cause electrodynamic forces and thermal stresses, which may need to be considered in the magnet mechanical design. This paper focuses on mechanical stress analysis during a quench of the 16 T cos-θ and block type dipole magnets. A finite element model allowed studying the stress due to the non-uniform temperature and current distribution in the superconducting coils. Two different CLIQ configurations were considered for the cos-θ design and one for the block type magnet. The analyses of the mechanical behavior of two magnets during a quench without or with hot spot turn were separately carried out. The simulation results show that the stress related to a quench should be considered when designing a high field magnet. [ABSTRACT FROM AUTHOR]

Simulating the transient effects occurring in superconducting accelerator magnet circuits requires including the mutual electro-thermo-dynamic interaction amongthe circuit elements, such as power converters, magnets, and protection systems. Nevertheless, the numerical analysis is traditionally done separately for each element in the circuit, leading to possible inconsistent results. We present STEAM, a hierarchical cosimulation framework featuring the waveform relaxationmethod. The framework simulates a complex system as a composition of simpler, independent models that exchange information. The convergence of the coupling algorithm ensures the consistency of the solution. The modularity of the framework allows integrating models developed with both proprietary and in-house tools. The framework implements a user-customizable hierarchical algorithm to schedule how models participate to the cosimulation, for the purpose of using computational resources efficiently. As a case study, a quench scenario is cosimulated for the inner triplet circuit for the high luminosity upgrade of the Large Hadron Collider at CERN. [ABSTRACT FROM AUTHOR]

In the framework of the EUROfusion DEMO project, design studies for the tokamak magnet systems are conducted across several European institutions. Superconducting magnets are required to generate the high magnetic fields needed for the plasma confinement and control. The reference conductor design is based on Cable-In-Conduit Conductors (CICC) cooled at cryogenic temperatures by forced circulation of supercritical helium. The proposed Toroidal Field (TF) coils Winding Pack (WP) design should satisfy the design/safety criteria during operation (e.g., minimal temperature margin) and in off-normal conditions (e.g., hotspot temperature). Quenches are studied to ensure that the proposed conductor design and associated quench protection system guarantee the integrity of the magnet; such events are a safety and investment protection issue, and as such deserve high levels of scrutiny. Quench propagation in a coil is a 3-dimensional (3D) problem. For this reason, a transient pseudo-3D modeling tool was developed for coupled thermal and thermo-hydraulic calculation in a tokamak superconducting coil. The coupling tool is based on a 1D model of the cable using the THEA code, considering current distribution, helium flow, thermal conduction in the strands and propagation of the quench along the conductor; the 2D transverse thermal diffusion across turns is modeled using the Cast3M code, considering the conductor jacket and insulation, on a selected set of cross-sections along the coil. The aim of the analysis is to assess the quench behavior of the CEA proposal for DEMO TF coil. The hotspot temperatures as well as the propagation of the normal zone along the conductor length are evaluated in a realistic quench scenario, taking into account the impact of transverse heat diffusion. [ABSTRACT FROM AUTHOR]

JT-60 SA is a fusion experiment which is jointly constructed by Japan and Europe and which shall contribute to the early realization of fusion energy, by providing support to the operation of ITER, and by addressing key physics issues for ITER and DEMO. In order to achieve these goals, the existing JT-60 U experiment will be upgraded to JT-60 SA by using superconducting coils. The 18 Toroidal Field Coils (TFC) of the JT-60 SA device are provided by European industry and tested in a Cold Test Facility (CTF) at CEA Saclay. At the summer 2017, 14 TFCs will have been tested at the nominal current of 25.7 kA and at a temperature between 5 and 7.5 K. The main objective of these tests is to check the TF coils performances and hence mitigate the fabrication risks. These tests allowed checking a certain number of performances of the TFCs: DC/AC insulation, cooling down characterization, RRR of the conductor, pressure drop in the winding pack, and temperature margin against a quench. This paper will show the testing program progress and give an overview of the main experimental results obtained during these tests. Themain performances of each coil will be summarized, analyzed, and discussed in the light of the expected TFCs performances. [ABSTRACT FROM AUTHOR]

The superconducting magnet system in Hall B being designed and built as part of the Jefferson Lab 12 GeV upgrade requires powering two conduction cooled superconducting magnets-a torus and a solenoid. The torus magnet is designed to operate at 3770 A and the solenoid at 2416 A. Failure modes and effects analysis determined that voltage level thresholds and dump switch operation for magnet protection should be tested and analyzed before incorporating into the system. The designs of the quench protection and voltage tap subsystems were driven by the requirement to use a primary hard-wired quench detection subsystem together with a secondary programmable logic controller (PLC)-based protection. Parallel path voltage taps feed both the primary and the secondary quench protection subsystems. The PLC-based secondary protection is deployed as a backup for the hard-wired quench detection subsystem and also acts directly on the dump switch. We describe a series of tests and modifications carried out on the magnet power supply and the quench protection system to ensure that the superconducting magnet is protected against all fault scenarios. [ABSTRACT FROM AUTHOR]

The superconducting toroidal field (TF) coils composed of a winding pack (WP) without radial plates, encapsulated in a steel casing, are currently being studied in the framework of the EUROfusion work package magnets (WPMAG). The ENEA (Italian National Agency for New Technologies, Energy and Sustainable Economic Development) 2014 TF WP design consists of graded (Nb3Sn + NbTi), double-layer wound rectangular cable-in-conduit conductors, for which the operational as well as accidental transients must be carefully investigated. This paper presents the analysis of the quench propagation inside the TF WP proposed in 2014 by ENEA using the state-of-the-art thermal-hydraulic code 4C. Different locations are considered for the quench initiation: 1) at the maximum temperature margin \Delta T\mathrm {mar}^{\mathrm {max}} , resulting in the most severe hotspot condition and 2) at the minimum temperature margin \Delta T\mathrm {mar}^{\mathrm {min}} , to analyze the most probable event. The evolution of voltage, normal zone, hotspot temperature, and maximum pressure in the TF WP is computed comparing the results from the two cases, highlighting the role of heat diffusion inside the TF WP. [ABSTRACT FROM AUTHOR]

Superconducting fault current limiters (SFCLs) are increasingly implemented in the power grid as a protection of substation equipment from fault currents. Resistive SFCLs are compact and light, however they are passively triggered and thus may not be sufficiently sensitive to respond to faults in the distribution grid. Here, we explore the prospect of adding an active management feature to a traditional resistive SFCL. A flexible radio-frequency coil, which is an integral part of the switching structure, acts as a triggering device. We show that the application of a short, 10 ms, burst of ac magnetic field during the fault triggers a uniform quench of the wire and significantly reduces the reaction time of the wire at low currents. The ac field burst generates a high density of normal zones, which merge into a continuous resistive region at a rate much faster than that of sparse normal zones created by the transport current alone. [ABSTRACT FROM AUTHOR]

Bulk materials of high-critical-temperature superconductors (HTSs) are promising for current leads and fault-current limiters because of negligibly small Joule heating under current transport and very low thermal conductivity. We consider that a Bi-2212 bulk superconductor prepared by the melt-casting process (MCP) is one of the best materials for these applications. In addition, MCP is well known to be a simple and economic process, and also served as a method for obtaining any sizes of HTS bulks consent to requirements for practical applications. In this paper, we present a study on the transport and quench properties of Bi-2212 bulk superconductors doped with \K2\CO3. First, the MCP samples doped with \K2\CO3 were analyzed by using an X-ray diffractometer and X-ray fluorescence spectrometry. In addition, the critical temperatures of the MCP samples doped with \K2\CO3 were observed. Then, we have investigated the relations between the critical current value and the doping quantity of \K2\CO3. The value of the direct-current critical current was determined at 77 K, and the self-fields derived from the electric field versus the transport current characteristics were obtained using a criterion of 1 \mu\V/cm. Finally, the alternating-current transport properties of the MCP sample were measured, and we have discussed the frequency dependence of the critical current with current distributions [ABSTRACT FROM PUBLISHER]

A superconducting quadrupole magnet with splittable yoke has been designed for use in ILC Main Linac (ML) cryomodules. The splittable yoke allows assembly around the beam pipe, to avoid potential contamination of the superconducting RF cavities. The magnet is cooled by conduction and covers the full range of required ML field gradients. A critical requirement is stability of the magnetic center, at the level of 5 \mu\m, for a 20% variation of the operating field. We report here the results of thermal, quench, and magnetic performance tests of a prototype splittable quadrupole, that were made up to the maximum design operating gradient in a conduction-cooled test cryostat. [ABSTRACT FROM PUBLISHER]

Abstract: A 9.4 T MRI superconducting magnet with a 800mm clear warm bore in diameter is designed and fabricated for bioscience research. The superconducting magnet consisting of five coaxial solenoid coils is fabricated with NbTi Wire-in-Channel (WIC) conductor where the ratios of copper to non-copper are from 5 to 10. The four compensation solenoid coils are with rectangular NbTi/Cu strand wires. The magnet will be operated in a relative low nominal current of 224.5A with a high level of stored energy, about 138MJ. A protection method with the cold diodes and resistors in series across the subdivided sections and active trigger heater to accelerate quench is adopted to avoid the damage of the magnet. In the paper, the quench simulation results of currents, voltages and hot-spot temperatures based on the protection scheme are analyzed in details. [Copyright &y& Elsevier]

Highlights: [•] Fault current limiter was used a high-speed interrupter. [•] High-speed interrupter was operated to bypass to the current limiter line. [•] The size of the fault current was limited to about 80% after the fault occurred. [•] The fault current was limited quickly within a half-cycle after the fault occurred. [ABSTRACT FROM AUTHOR]

Highlights: [•] We modeled the central clock-wise pancake of JT-60SA TF magnet at the EOB. [•] We simulated a quench followed by a fast discharge. [•] We evaluated the temperature and pressure rises in the nominal configuration. [•] We evaluated the effect of several parameter changes on the thermal-hydraulic response of the system. [Copyright &y& Elsevier]

Abstract: The FAIR project undertaken at GSI (Darmstadt, Germany) will lead to the construction of 2 superconducting synchrotrons and one superconducting fragment separator called Super-FRS. This paper presents quench measurements and calculations on the FAIR Super-FRS dipole using two different 3D FEM programs. The first (called Opera Quench) gives the same order of propagation velocities as those computed with a 1D program. The second (developed by CIEMAT) succeeds to reproduce the current drop and quench resistance measured on the Super-FRS dipole. [Copyright &y& Elsevier]

Cables in superconducting magnets are subjected to field-dependent losses, i.e., induced interstrand and interfilament coupling losses, and superconductor hysteresis losses. For the two kinds of induced eddy currents, analytical and numerical models are available, allowing calculating the dissipated power under various operating conditions. For the losses stemming from the superconductor magnetization, the literature only gives formulas for the dissipated energy over closed excitation cycles. We derive an expression for the instantaneously dissipated hysteresis losses during an arbitrary ramp profile using a simplified geometry and hysteresis model. This allows estimating the losses dissipated in nonclosed excitation loops. [ABSTRACT FROM PUBLISHER]

MICE superconducting spectrometer solenoids fabrication and tests are in progress now. First tests of the Spectrometer Solenoid discovered some issues which could be related to the chosen passive quench protection system. Both solenoids do not have heaters and quench propagation relied on the “quench back” effect, cold diodes, and shunt resistors. The solenoids have very large inductances and stored energy which is 100% dissipated in the cold mass during a quench. This makes their protection a challenging task. The paper presents the quench analysis of these solenoids based on 3D FEA solution of coupled transient electromagnetic and thermal problems. The simulations used the Vector Fields QUENCH code. It is shown that in some quench scenarios, the quench propagation is relatively slow and some areas can be overheated. We describe ways of improving the solenoids' quench protection in order to reduce the risk of possible failure. [ABSTRACT FROM PUBLISHER]

We propose a new structure of superconducting fault current limiters (SFCLs) coupled with a conventional transformer. The proposed SFCL systems have structures that the primary winding and the secondary winding of a transformer are connected with normal power grids and the tertiary winding of a transformer is connected with superconductors. These structures have advantages of both a transformer type SFCL and a resistive type SFCL. Therefore our SFCL can easily control the current limiting ratio by variation of the turn number of a transformer and minimize quantity of superconductors. Also it can be invisible in normal power grids and not bulky structure unlike a transformer type SFCL or a flux-lock type SFCL. Experimental results are reported in terms of current limiting properties, fault voltages and quench characteristics of superconductors in this system. [ABSTRACT FROM PUBLISHER]

In this paper we analyse numerically and experimentally the quench behavior of Cu-stabilized second-generation high temperature superconducting (2G HTS) wires at self-field and in adiabatic conditions. The electric field profiles along the superconductor after applying an energy pulse to the conductor have been obtained together with the parameters characterizing the quench: minimum quench energy (MQE) and the normal zone propagation velocity (NZPV). The analysis has been performed at different temperatures, T, between 72 K and 77 K, and at different applied currents, I/Ic(T)<1, Ic being the critical current. Our analysis shows that the numerical results obtained by finite element method (FEM) are closer to the experimental MQE values when the contribution of the thermal mass of the heater is taken into account. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the situation where a mesoscopic 1D ring or 2D cylinder is subject to a magnetic field by simulating the time dependant Ginzburg–Landau equations with periodic boundary conditions. We investigate the different possible evolutions for the 1D phase slip phenomenon. The case of the multiple phase slips is analyzed in details and we study the competition between simultaneous and consecutive multiple phase slips analytically and numerically. In 2D we study the creation of vortex–antivortex pairs. Following the theory of the Kibble–Zurek mechanism, we quenched the sample by applying a strong current and observe vortex–antivortex pairs dynamics. [ABSTRACT FROM AUTHOR]

An active quench protection system is developed to safely protect a 1.5 T superconducting MRI magnet. The protection system includes a digital quench detection controller, a set of quench heaters and voltage taps, a battery backed DC power supply and solid-state switches. The quench controller takes the voltage signals from the voltage taps over superconducting coils and monitor a quench onset. To distinguish a quench signal from operational signals, the quench controller uses a pre-determined moving average voltage over 50 ms as the threshold signal for quench detection. The threshold signal is more than 10 times larger than any of the normal operation signals to avoid false quenching. Once detected moving average voltage exceeds the threshold, the quench controller will close solid-state relays and power quench heaters to accelerate the quench propagation over the entire magnet. The system has been tested in a MRI magnet test module. [ABSTRACT FROM AUTHOR]

Quench experiments were performed in the CEA Saclay facility on the Seht superconducting magnet. The Seht facility is part of the Iseult R&D program. Seht is an 8-T coil wound in sixty double pancakes using NbTi conductor. The coil is cooled by steady state superfluid helium at 1.8 K and 1.2 bar. Instrumentation, inside the coil and in the helium bath, includes voltage taps, pressure and temperature sensors, as well as flow meters. The major issues in the Seht experiments will be addressed here: the normal zone propagation in the coil during quench and the pressure and temperature rise in the helium. [ABSTRACT FROM AUTHOR]

This paper presents coupled transient thermal and electromagnetic finite element analysis of quench in the Q2, Q3, and dipole superconducting magnets using Vector Fields Quench code. Detailed temperature distribution within coils and aluminum force collars were computed at each time step. Both normal (quench with dump resistor) and worst-case (quench without dump resistor) scenarios were simulated to investigate the maximum temperatures. Two simulation methods were utilized, and their algorithms, implementation, advantages, and disadvantages are discussed. The first method simulated the coil using nonlinear transient thermal analysis directly linked with the transient circuit analysis. It was faster because only the coil was meshed and no eddy current was modeled. The second method simulated the whole magnet including the coil, the force collar, and the iron yoke. It coupled thermal analysis with transient electromagnetic field analysis which modeled electromagnetic fields including eddy currents within the force collar. Since eddy currents and temperature in the force collars were calculated in various configurations, segmentation of the force collars was optimized under the condition of fast discharge. [ABSTRACT FROM AUTHOR]

To achieve the effective performance of the flux-lock type superconducting fault current limiter (SFCL), the countermeasures to improve the recovery characteristics of the flux-lock type SFCL are required. In this paper, as one of the solutions, the method using a superconductor's trigger when the quench in the high-TC superconducting (HTSC) element occurred was suggested. To verify the suggested method in case of the fault occurrence, the control circuit to detect the quench of HTSC element and the current limiting resistor (CLR) to limit the fault current were designed and fabricated. With the fabricated control circuit and the CLR, the fault current limiting and recovery characteristics of the flux-lock type SFCL using the suggested method were tested. Through the analysis for the experimental results, the recovery characteristics of the flux-lock type SFCL could be confirmed to be improved than the SFCL not using the superconductor's trigger. [ABSTRACT FROM AUTHOR]

We analyse the issues of quench propagation in the NbTi Poloidal Field Conductor Insert (PFCI), recently tested at JAEA Naka, Japan. The simulation tools Mithrandir, already validated against data from previous Nb3Sn Insert Coils, and M3, implementing a more detailed thermal-hydraulic description of the CICC cross section, are used. The results of the analysis are reported in the paper and compared with experimental data, with particular attention to NbTi versus Nb3Sn features and to the effects of different model assumptions. [ABSTRACT FROM AUTHOR]

A superconducting coupling solenoid mounted around four conventional RF cavities, which produces up to 2.6 T central magnetic field to keep the muons within the cavities, is to be used for the Muon Ionization Cooling Experiment (MICE). The coupling coil made from copper matrix NbTi conductors is the largest of three types of magnets in MICE both in terms of 1.5 m inner diameter and about 13 MJ stored magnetic energy at full operation current of 210 A. The stress induced inside the coil assembly during cool down and magnet charging is relatively high. In order to validate the design method and develop the coil winding technique with inside-wound SC splices required for the coupling coil, a prototype coil made from the same conductor and with the same diameter and thickness but only one-fourth long as the coupling coil was designed and fabricated by ICST. The prototype coil was designed to be charged to strain conditions that are equivalent or greater than would be encountered in the coupling coil. This paper presents detailed design of the prototype coil as well as developed coil winding skills. The analyses on stress in the coil assembly and quench process were carried out. [ABSTRACT FROM AUTHOR]

The quench detection system in ITER superconducting magnet systems is a real challenge for the poloidal field (PF) system and the central solenoid (CS) due to their fast-pulsed operation. An existing CEA code allowing very precise magnetic field calculations in tokamaks (Traps) has been upgraded (TrapsAv) to calculate the inductive voltages induced across any coil sub-element during a plasma scenario. The envisaged primary detection system is based on voltage measurements. For the CS, a detection system is proposed and discussed based on the central difference average balance of 3 neighboring double pancakes. For the TF system, the presently considered compensation circuit in ITER is a strip co-wound on to the conductor. A simple analytical calculation is proposed to estimate the voltage during a plasma disruption or during the scenario across the co-wound strip and across the conductor as well, due to the toroidal component of the plasma current. [ABSTRACT FROM AUTHOR]

Abstract: In the first-peak non-limiting type superconductor-triggered fault current limiter (STFCL), which was developed by the collaborative work of KEPRI and LSIS, the first half cycle of fault currents is passed, unlimited. Due to these characteristics, information needed for the fault judgments can be provided to the protection relays, which is useful for the protective coordination of power system. In this fault current limiter, superconductors are used as a fault detector that does not generate resistive loss in normal operation state. Therefore, high Jc and fast occurrence of large resistance are the essential properties of superconductors for the application to fault detectors. In this study, for the design of superconducting fault detector (SFD), we investigated the quench behavior of two kinds of superconductors, stabilizer-free coated conductors (SF-CC) and Au/YBCO/sapphire substrate, during the operation of the first-peak non-limiting type STFCL. The dimension of SF-CC was 12mm wide×1000mm long and that of Au/YBCO/sapphire was 20mm wide×100mm long. Their critical current (Ic) values were 250A and 200A, respectively, and the critical temperature (Tc ) was both 90K for both superconductors. When fault currents of over 3kA were applied, the STFCL carried out the current limitation successfully. At the beginning of the quench, SF-CC generated a resistance of 150mΩ, and 394mΩ was generated in the Au/YBCO/sapphire substrate, when 150Vrms was applied. After the first half cycle, the resistance of the superconductors increased up to 263mΩ, and 846mΩ, respectively, and the temperature reached 132K and 127K. In addition, we also investigated the recovery characteristics of the SFDs. The SF-CC and Au/YBCO/sapphire substrate recovered the superconductivity by 353ms and 357ms, respectively. Based on the results of the analysis, we determined the required length of the superconductors for the SFD application. [Copyright &y& Elsevier]

Superconducting power devices are considered for many applications, including airborne applications. For the devices of interest the operating temperature needs to remain around 70 K in order to minimize the weight and volume of the associated cooling system. The use of YBa2Cu3Ox (YBCO) coated conductors allows for operation at fairly high temperature (65-77 K) while maintaining high current carrying capabilities. Unfortunately, when a hot spot is created in a coated conductor wound magnet, the quench propagates so slowly that it cannot be detected using conventional methods and therefore those magnets may remain unprotected. To address this quench detection issue, we must better understand the physics of the quench and the phenomena that drive it so it can be accurately simulated. We have modeled YBCO tapes using Finite Element Analysis to assess the role of the contact resistance between the different layers composing the tape. Indeed, if the temperature rises, the YBCO layer becomes highly resistive and the current redistributes into the stabilization layers. The contact resistance between the YBCO layer and the copper is likely to play a very important role in terms of the current sharing length and voltage difference between the layers. This paper presents a model implemented in COMSOL Multiphysics, simulation results and a discussion. [ABSTRACT FROM AUTHOR]

A new quench monitoring system by using the Poynting Vector method was proposed. This new system can indirectly detect normal transitions which are suddenly induced during an operation of superconducting coils. In this system, the superconducting coil is surrounded by the thin metallic cylinder composed of several pieces, where the cylinder is electrically insulated from the coil; potential leads to measure local electric fields are directly attached to this cylinder surface and pickup coils to measure local magnetic fields are put on the surface. The Poynting vector distribution around the coil can be obtained by using many sets of both the potential lead and the pickup coil. Since sudden changes of energy flow profiles around the superconducting coil are induced in the event of local normal transitions of the coil winding, such an event of coils can be detected by the change of the Poynting vector. This system has no risk of the destructive voltage breakdown which may happen in case of the existing balance voltage method, because there is no need of direct contacts on the coil windings. In addition, this method is expected to be higher reliability and sensitivity than the acoustic emission method. A demonstration test was carried out of monitoring the quench for the Bi-2223 coil partially immersed in liquid nitrogen, and a sign of normal transitions before the quench was successfully detected by this method. [ABSTRACT FROM AUTHOR]

The superconducting (SC) fault current limiter (FCL) is very attractive to enhance the security and the power quality. of the electricity grid, so its great interest throughout the world. Most of SC FCL uses the quench of a SC element and the thermal phenomena are fundamental. We study them with two approaches: experiments and calculations. For the experiments, we have developed temperature sensors deposited directly on coated conductors to achieve the best thermal coupling and a very short time response. The sensors are micron size copper meanders. A very thin polymer layer provides the electrical isolation. The sensor performances are very satisfying both in terms of time response and accuracy. The measurements are in good agreement with temperature calculations, performed using the current data during limiting experiments. The recovery phase is very important and has been studied using the temperature measurements. The cooling conditions such as bath temperature play an important part for the recovery. Several tests carried out on different samples are presented and analysed. These works are important for a better understanding of the complex phenomena occurring during a limitation and for the design of a conductor suitable for FCL. [ABSTRACT FROM AUTHOR]

To protect the KSTAR (Korea Superconducting Tokamak Advanced Research) superconducting coils against a quench, the quench detection system based on voltage measurement was fabricated. It used a detect/dump scheme which detects the presence of non-recovering normal zones and activates a dump circuit that transfers most of the stored energy into a dump resistor. Even though it is desirable to discharge the coil energy as fast as possible after quench detection, a time delay between the quench detection and the complete dump circuit actuation will be necessary in order that the quench voltage is to be distinguished from various noises. The quench threshold voltage and the delay time should be set before operation for quench voltage detection so that the maximum hot-spot temperature could be limited to 150 K. This paper describes the hardware techniques to prevent the malfunction of the quench detection due to voltage noises arising from the KSTAR operating scenarios. During the first operation of the KSTAR machine, the inductive voltages and other voltage noises were measured and effectively compensated below voltage thresholds. A quench did not occur and the quench detection system was well operated without any false activation. [ABSTRACT FROM AUTHOR]

To achieve the first plasma of the Korea superconducting tokamak advanced research (KSTAR), the KSTAR superconducting coils were tested in advance. As they should operate in excessively low temperature of 4.5 K and high magnetic field environment of 7.5 T, it is crucial to monitor the cryogenic and the structural behaviors of KSTAR device during the commissioning period including a cool-down. The temperatures of the KSTAR toroidal field (TF) coil and the poloidal field (PF) coils were measured during the entire operating period. The mechanical stresses on the TF and PF structures were continuously monitored to check if they go beyond the limiting value calculated through the simulation. The alignment of the KSTAR device was checked by using displacement sensors. The TF coils were successfully supplied with 15 kA DC current for 8 hours, and the maximum 5 kA/s current variation of the PF coils were tested. For the main experiment, the interlock test of the quench detection system for the KSTAR coils was carried out at reduced currents of 1 kA. From these results the quench protection circuit, and the current-flow of the KSTAR superconducting coils proved to be well performed for the first plasma operation. [ABSTRACT FROM AUTHOR]

The superconducting coupling solenoid to be applied in the Muon Ionization Cooling Experiment (MICE) is made from copper matrix Nb-Ti conductors with inner radius of 750 mm, length of 285 mm and thickness of 102.5 mm at room temperature. The magnetic field up to 2.6 T at the magnet centerline is to keep the muons within the MICE RF cavities. Its self inductance is around 592 H and its magnet stored energy is about 13 Mi at a full current of 210 A for the worst operation case of the MICE channel. The stress induced inside the coil during cool down and charging is relatively high. Two test coils are to build and test in order to validate the design method and develop the fabrication technique required for the coupling coil winding, one is 350 mm inner diameter and full length same as the coupling coil, and the other is one-quarter length and 1.5 m diameter. The 1.5 m diameter coil will be charged to strain conditions that are greater than would be encountered in the coupling coil. This paper presents detailed design of the test coils as well as developed winding skills. The analyses on stress in coil assemblies, AC loss, and quench process are carried out. [ABSTRACT FROM AUTHOR]

A small high-temperature superconductor (HTS) coil was designed and tested at the General Electric Global Research Center to evaluate the overcurrent capability for the HTS generator rotor. The superconducting rotor coil is a layer-wound racetrack coil using the BSCCO 2223 conductor. Overcurrent simulation tests have been done to simulate the fault operation condition for the generator based on previous analysis work. The obtained data are used to evaluate the performance of the HTS material in generator applications. [ABSTRACT FROM AUTHOR]

Two Cu stabilized Nb3Al strands, F1 (Nb matrix) and F3 (Ta matrix), fabricated at NIMS were wound into Rutherford cables at Fermilab in collaboration with NIMS. A Small Race-track magnet using F! Rutherford cable, the first Nb3Al dipole magnet in the world, was constructed and tested to full current at Fermilab. This magnet was tested extensively to full short sample data and its quench characteristics were studied and reported. The 3-D magnetic field calculation was done with ANSYS to find the peak field. The quench characteristics of the magnet are explained with the characteristics of the Nb3 Al strand and Rutherford cable. The Small Racetrack magnet built using Ta matrix F3 strand was constructed and will be tested in the near future. The advantages and disadvantages of these Nb3Al cables are briefly discussed. [ABSTRACT FROM AUTHOR]

The integrated three-phase flux-lock type superconducting fault current limiter (SFCL) consists of three-phase fluxlock reactor wound on an iron core with the same turn's ratio between the primary coils and the secondary coils for each phase. When a SFCL is operating under normal condition, and assuming that the leakage flux is neglected, the magnetic flux generated between the primary and the secondary coils of each phase is canceled out perfectly. Therefore, the impedance of the SFCL is zero and the power system can operate normally without any loss. However, when a fault occurs, quench happens in high-TC superconducting (HTSC) elements and the magnetic flux generates in an iron core. Therefore, the impedance of the SFCL is large enough to limit fault currents. In this paper, we investigated the fault current limiting characteristics according to the fault angle in SFCL in fault types such as the single-line-to-ground fault, the double-line-to-ground fault and the triple-line-to-ground fault. Experiment results show that the fault current limiting characteristics of the SFCL are dependant on the quench characteristics of HTSC elements in each phase. [ABSTRACT FROM AUTHOR]

Performance of fault current limiter demonstrators based on either a single coated conductor (CC) tape or CC assemblies tested in current limitation modus is reported. A primary goal of this work was to achieve a quick reaction of the fault current limiter (FCL) device, and to study possibilities to provide a reliable and controllable time performance of limiting devices. An improved homogeneity of coated conductors was achieved employing a new alternating beam assisted deposition technique. This technique was used for processing of biaxially textured buffer layers with enhanced quality. Typically, the tapes yielded a critical current of 200–300 A per cm width at 77 K and self field. In demonstrators based on single CC tape, a 10 μs transient time of quench was observed. A stack of coated conductors jointed in parallel was employed as an active FCL element. Two alternative cases are studied when (i) CC tapes exhibit an equal and homogeneously distributed critical current and (ii) the critical currents and contact resistances are different in different tapes. As a result, it was experimentally shown that the quench duration can be varied from 10 μs (in case (i)) to 2 ms (in case (ii)). Such artificially smoothed quenches with pre-determined time dependence should play an important role in AC and DC networks where current surges have to be reliably suppressed. We found that the quenching behavior of the entire electrical circuits is consistent with a finite element model that takes into account a non-linear type of resistivity of CC tape. Short recovery time of 05 ms was achieved in CC based fault current limiters. [ABSTRACT FROM AUTHOR]

A superconducting fault current limiter could play a very important role in DC networks. The new electric energy landscape opens the way for new network diagrams with such DC buses. One key issue is that the whole superconductor participates to the limitation process in order to avoid destructive local hot spots. We propose to operate close to the critical temperature to benefit from higher quench homogeneity in the electric field development along the superconductor. We present limitation experiments in function of the temperature for two lengths (0.23 and 2 m) based on the IBAD-YSZ processing route with a stainless steel substrate and a gold shunt. The architecture of the conductor leads to shunt damages at the edges of the tape. Temperature sensors (resistive coating) have been deposited directly on sapphire wafers with YBCO in order to measure the temperatures. These sensors show a sufficient time response and sensitivity. The agreement is rather good with the simulations. [ABSTRACT FROM AUTHOR]

As well known, an inrush current of transformer reaches about several times larger than the rated current. When such a large inrush current flows into a superconducting transformer, it will induce a quench of superconducting windings. In this paper, we fabricated a small experimental superconducting transformer, and investigated the behavior of superconducting winding against the inrush current. The experimental result shows that a superconducting winding quenches for such a large inrush current, but it returns quickly to superconducting state in few cycles spontaneously. [ABSTRACT FROM AUTHOR]

When a synchronous generator connected to the power grid experiences a fault, it is required to stay on line, ride through the fault, and be able to carry full rated field current when the fault is cleared. The peak current during these events could be 2 times higher than the normal operating current. This may cause an HTS rotor coil to go into normal state and generate Joule heating. If the fault event is short enough and the heat dumped can be carried away by the cooling system, the coil may recover to the superconducting state at the end of the fault. Otherwise, the coil may thermally run away, or ‘quench’. To investigate the quench behavior of the HTS rotor coil of the 100 MVA generator at GE Global Research Center, a 1.5 MVA prototype coil was developed and tested to quench under different conditions. The experiment design, set up, tests and test results are presented in this paper. [ABSTRACT FROM AUTHOR]

This paper presents two-stage high-power mechanical-thyristor switches developed as 40-kA direct current (dc) circuit breakers for the superconducting coil energy dump system of Korea superconducting Tokamak advanced research (KSTAR). An advanced switching system used in the quench protection should allow multishot mode of operation without maintenance and long lifetime with arcless dc current commutation. The system is designed to combine the advantages of the both mechanical and solid-state power switches. The mechanical stage is to conduct dc current for normal superconducting coil operation and the thyristor stage is to provide fast arcless dc current interruption for quench protection (QP). Compared with the all solid-state switches and vacuum interrupters of equal capabilities the pro- posed switch is much cheaper than the dc breakers and has lower power dissipation in current conducting state ‘Kuchinski et at. in Proc. Power Ele., 899–903, 1995;’ ‘Benfatto et aL IEEE Power Del., Vol. 3, No. 4, pp. 1372–1376, Oct. 1998.’ Also, it is much faster than the vacuum interrupters. The system is designed to break 40-kA dc current within 200 ms. Also, KSTAR device, a configuration of the energy dump system and coil power supplies are presented. [ABSTRACT FROM AUTHOR]

Abstract: We address the use of coated conductors for resistive fault current limiters. Fast quench propagation is essential to let the conductor switch on the full length within milliseconds. The ordinary quench propagation mechanism, however, is too slow because of the small heat diffusivity in typical tape substrate materials. Here we present a new mechanism, which is not based on heat diffusion, but on a conductor geometry that leads to current bunching and a rapid spreading of the resistive state. Thus, the conductor develops its full normal resistance, is homogenously warming further up, and self-protecting without the use of thick normal conducting stabilizers that reduce the efficiency. The mechanism was confirmed by a numerical simulation and by experiments on samples of short and medium length. Tape samples up to 50cm length switched homogenously exhibiting a maximum voltage drop of 2.7V/cm. [Copyright &y& Elsevier]

The CMS experiment (Compact Muon Solenoid) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting magnet with 6 m diameter by 12.5 m long free bore, enclosed inside a 10000 ton return yoke. The magnetic field is achieved by a 4-layer superconducting solenoid made of a reinforced Rutherford type superconductor with a hybrid configuration and wound inside an external aluminum cylinder. The coil is indirectly cooled at an operating temperature of 4.5 K by a thermosiphon, and it is designed to run at a nominal current of 20 kA. The corresponding maximum stored magnetic energy reaches 2.6 GJ with an E/M ratio of 12 kJ/kg. The quench protection is achieved by discharging the magnet in an external resistor in fast mode, with a peak voltage in the coil kept at 600 V and a voltage to ground of ±300 V during the discharge. The coil design takes benefit of the quench back effect to limit the temperature gradients inside the winding pack in case of quench. The design and the characteristics of the quench protection system are described. The computational results of the quench protection for several operating currents are presented. The behavior of the magnet in case of faulty conditions on the protection system is analyzed. [ABSTRACT FROM AUTHOR]

A thin superconducting solenoid has been constructed for ATLAS, one of the four LHC experiments at CERN. The single layer coil wound with an AI stabilized NbTi superconductor, with overall dimensions of 5.3 m length and 2.6 m diameter and operating at 7.6 kA provides the 2 T magnetic field for the inner detector. The coil was successfully tested at the company before shipment and re-tested at CERN on surface in its final configuration before commencing the installation in the ATLAS cavern 100 m underground. The tests include an extensive study of the quench evolution and in particular the normal zone propagation through the coil windings and in the superconducting bus-lines. A special feature of this coil is the use of aluminum quench propagation strips glued to the windings inner surface. This design enhances the turn-to-turn normal zone propagation velocity, reaching up to 0.8 m/s, and limits the hot spot temperature to 110 K. Along the conductor, normal zone propagation reaches velocities up to 14 m]s at nominal current. [ABSTRACT FROM AUTHOR]

We investigated the quench development in resistive superconducting fault current limiters (SFCLs) with a protective coating. The protective coaling is needed to protect the SFCL from moisture in the air, but should not have an adverse effect on the quench properties of the films. The 300 mn thick YBCO film coated in situ with a gold layer was first patterned into meander lines by photolithography, and then coated with teflon by spin-coating. The SFCL was subjected to simulated AC fault currents for quench measurements. It was immersed in liquid nitrogen during the experiment for effective cooling. The coating retained its form throughout repeated quenches in liquid nitrogen. Moreover, quench properties did not change for thin coatings. The quench resistance of SFCLs with a protective coating was similar to that without a coating. This enables one to use a protective coating without compromising the performance of SFCLs. The quench development in SFCLs with a coating of different thickness was explained with the concept of heat transfer to the coating and the liquid nitrogen. [ABSTRACT FROM AUTHOR]